Fast, but not the fastest.
My personal minimum is pyfty's surrender at 4-th turn, but it doesn't count.
So, 5 turns was fastest for me.
http://i49.tinypic.com/2cfw6pv.jpg
After last update i was not able to repeat, but i made 6-turn game.
http://i48.tinypic.com/b7gbo6.jpg
Just ordinary blitzkrieg deck.